I’m trying to find a flashlight that runs on one 18650 battery that will last about 3 hours on high. I’m looking for something in the 1000 lumens range or higher would be nice thank you! I know most flashlights will have a step down after a few minutes. I’m looking for one that isn’t that much of a step down.
You can not get 1000 lumens for 3 hrs with a single 18650 cell. Lower your lumens requirements or be prepared to change cells once or twice.
The best 18650 have around 12 Watt/hour of energy, a high bin XP-L needs at least 3 amps at around 3.5v to give 1000 lumens, that’s aroud 10.5 Watts, best case scenario gives around 1 hour of 1000 lumens from a 18650.
What he said
Achieving 1000 lumens (LED lumens) from most emitters requires somewhere in the 3 amp range, so to run for 3 hours would require about 9000 mAh. The biggest 18650s are 3600 mAh, so not even close.
All of that is a rough simplistic estimate, by the way. Real world performance may require even more due to heat loss, etc.
I have a MH20 that runs for 2 1/2 hours on high, I know that there is a step down in brightness after a few minutes. I was wondering if there is another flashlight with a better performance that that, on a single cell.
Yep. If you check back in a few years, it’s likely batteries will hold more energy and light sources will be more efficient.
You should also think about whether you want a regulated driver that holds the light’s brightness stable as long as possible then goes dim fast and then dark — or one that dims slowly over time as the battery drains down.
Best case is 1-1.2A for 3 hours, which is roughly 3.5 watts or 350-400 lumens minus losses from the lens and reflector. 250 is a reasonable expectation.
You could go with a multi-cell light like the SR52 or SR52UT to get that kind of runtime or better at 1000 lumens.
Probably the very best 1x18650 light is the Zebralight SC600w III HI.
It uses an XHP35 HI LED and has a temp sensor for thermal stepdown. It will produce around 200-400 lumens for 3 hours, or 1200 lumens for short bursts.
No LED light available today will sustain 1000+ lumens for 3 hours on a single 18650. The only light I now of that can run 3 hours on max offhand is the Zebralight SC62d. You’ll only get 300 lumens or so max though.
If you really want to run at 1000+ lumens for 3 hours you’re going to need to buy a coke-can sized 4x18650 light.
I’ve been looking at the Zebralights. The SC600w III HI is probably the one I’ve been looking at the most. Thank you everyone for all the information.
I did a review of the SR52-UT a while back, including a runtime test. Using 3x 3400 mAh Panasonic NCR18650B cells, I got just over 150 minutes on high before the low voltage light came on, and by that time it had dropped to almost half its initial output. So even though its a 3x18650 light it didn’t even come close to meeting the OP’s requirements.
Here’s that graph, if anyone is curious:
My bad. The multi-cell light reco still stands if OP wants 1000+ lumens for that length of time, but just not the ones I mentioned I guess. 
What about this new battery that comes with the Nitecore TM03 Nitecore NL18650D Dedicated Battery (TM03 Only). Will we see flashlights moving in this direction to get more lumens OR runtime.
Nitecore just puts a wrap on existing batteries form korea or japan (hopefully not china), the NL18650D doesn’t even have the best capacity, it’s a trade of between capacity and high current drain aptitude.